In the development of radio communication systems, such as mobile communication systems (like for example GSM (Global System for Mobile Communication), GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunication System) or the like), efforts are made for an evolution of the radio access part thereof. In this regard, the evolution of radio access networks (like for example the GSM EDGE radio access network (GERAN) and the Universal Terrestrial Radio Access Network (UTRAN) or the like) is currently addressed in research and development as well as in standardization. Accordingly, such improved radio access networks are sometimes denoted as evolved radio access networks (like for example the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) or as being part of a long-term evolution (LTE). Although such denominations primarily stem from 3GPP (Third Generation Partnership Project) terminology, the usage thereof hereinafter is not intended to limit the respective description to 3GPP technology, but is rather intended to generally refer to any kind of radio access evolution irrespective of the specific underlying system architecture.
In the following, for the sake of intelligibility, LTE (Long-Term Evolution according to 3GPP terminology) is taken as a non-limiting example for a radio access network being applicable in the context of the present invention and its embodiments. However, it is to be noted that any kind of radio access network may likewise be applicable, as long as it exhibits comparable features and characteristics as described hereinafter.
The radio interface in LTE (or E-UTRAN) is based on Orthogonal Frequency Division Multiple Access (OFDMA), which is one exemplary modulation scheme applicable for broadband radio access (or other radio access technologies). In the downlink direction of the LTE (or E-UTRAN) radio interface, there are defined a Physical Downlink Shared Channel (PDSCH) and a Physical Multicast Channel (PMCH) as downlink data channels, as well as a Physical Downlink Control Channel (PDCCH), a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid Indicator Channel (PHICH), a Physical Broadcast Channel (PBCH) and Primary and Secondary synchronization channels (SCHs) as downlink control channels. In the uplink direction of the LTE (or E-UTRAN) radio interface, there are—among others—defined a Physical Uplink Shared Channel (PUSCH) and a Physical Uplink Control Channel (PUCCH).
In the following, mainly the downlink case is described in detail, while the principles set out in this regard are analogously applicable to the corresponding uplink channels in the uplink case.
The resource mapping of the downlink channel types depends on the downlink system bandwidth (N_DL_RB), which may be used as a configuration parameter and represents the available number of downlink resource blocks (RBs) constituting a resource grid for a multiple access scheme.
According to the present LTE example, the Physical Control Format Indicator Channel (PCFICH) is used to broadcast the number of OFDM symbols used for control signalling purposes by the PDCCH control channel (i.e. 1, 2, or 3). The PCFICH information consists of 32 bits coded into 16 QPSK modulation symbols (QPSK: Quadrature Phase Shift Keying) which are mapped in the first OFDM symbol of a subframe as four symbol quadruplets to four resource element (RE) groups (of consecutive subcarriers), wherein these resource element groups are equally distant to each other in the frequency dimension. The position of the four resource element groups varies with the physical cell identifier such that basically all possible resource element group positions can be reached by the resource mapping of the PCFICH control channel. For details of the PCFICH resource mapping, reference is made to the specification document 3GPP TS 36.211 v 8.3.0, Chapter 6.7.4.
As a result, the PCFICH control channel according to current specification practically extends over the complete carrier frequency spectrum.
According to the present LTE example, the Physical Hybrid Indicator Channel (PHICH) contains positive and negative acknowledgements (ACK/NAKs) corresponding to uplink transmissions, i.e. for the uplink hybrid automatic-repeat-request (HARQ). The PHICH is assigned to three resource element (RE) groups whose positions depend on the downlink system bandwidth (N_DL_RB), the resource element groups already covered by the PCFICH control channel, on the Hybrid ARQ group index, the physical cell identifier, and the frame structure. Assuming a typical allocation, the PHICH is allocated to the first OFDM symbol or in the first three OFDM symbols in each subframe and spread in three portions over the carrier bandwidth. For details of the PHICH resource mapping, reference is made to the specification document 3GPP TS 36.211 v 8.3.0, Chapter 6.9.3.
As a result, the PHICH control channel according to current specification practically extends over the complete carrier frequency spectrum.
According to the present LTE example, the Physical Downlink Control Channel (PDCCH) contains uplink and downlink control information, i.e. scheduling assignments. By way of these user equipment-specific control information, the allocations on a data channel (e.g. PDSCH) are defined for the respective user equipment. The PDCCH is built from control channel elements (CCEs) and maps (except for resources used by the PCFICH and PHICH control channels) to the entire configured downlink system bandwidth (N_DL_RB) for the first up to the first three OFDM symbols of a subframe. According to current specification, there are four PDCCH format types referring to four different control channel element (CCE) aggregation levels (i.e. to four different numbers of CCEs being associated with the respective PDCCH format type, namely 1, 2, 4, or 8). For details of the PDCCH resource mapping, reference is made to the specification document 3GPP TS 36.211 v 8.3.0, Chapter 6.8.5.
As a result, the PDCCH control channel according to current specification is distributed over the complete carrier frequency spectrum (depending on the user equipment identifier) in order to support blind decoding by the user equipment.
Each user equipment scheduled in a considered subframe—whether in downlink or in uplink—requires a downlink control information (DCI) element in the PDCCH control channel. The size of the DCI element depends on the DCI format, the downlink and uplink bandwidth configuration (N_DL_RB and N_UL_RB), as well as a resource size parameter P. In the following, the presently specified DCI formats and sizes are summarized.
Format 0
Scheduling/Control Purpose: PUSCH
Variation parameter: N_UL_RBs
Format 1, 1A, 1B, 1C
Scheduling/Control Purpose of Format 1: PDSCH SIMO, TX diversity, Beamforming
Scheduling/Control Purpose of Format 1A: Compact PDSCH Single Antenna, TX diversity, Beamforming
Scheduling/Control Purpose of Format 1B: PDSCH Closed Loop TX diversity
Scheduling/Control Purpose of Format 1C: Scheduling grants for BCCH, RACH, and Paging responses
Variation parameter: N_DL_RBs, P
Format 2, 2A
Scheduling/Control Purpose: PDSCH Open Loop/Closed Loop Spatial Multiplexing
Variation parameter: N_DL_RBs, P
Format 3, 3A
Scheduling/Control Purpose of Format 3: TPC for 2 bit Power Control on PUCCH/PUSCH
Scheduling/Control Purpose of Format 3A: TPC for 1 bit Power Control on PUCCH/PUSCH
In the above, PUSCH stands for Physical Uplink Shared Channel, PUCCH stands for Physical Uplink Control Channel, SIMO stands for single-input-multiple-output, TX stands for transmission, BCCH stands for Broadcast Control Channel, RACH stands for Random Access Channel, and TPC stands for Transmit Power Control.
In view of the above, according to the present LTE example, while the PBCH and the Primary and Secondary SCH are centered with regard to the downlink carrier using a narrow bandwidth of six resource blocks (RBs), the PDCCH, the PCFICH and the PHICH extend over the complete downlink system bandwidth, as configured by the parameter N_DL_RB. The PDSCH and the PMCH allocations, i.e. the data channel allocations, are controlled by scheduling.
Since the control channels, for example those mentioned above, conventionally have allocation positions (resource mappings) ranging over the complete available frequency spectrum, no arbitrary downlink system bandwidth scaling is feasible.
The LTE downlink system bandwidth could be configured, if all options for N_DL_RB ranging from 6 RBs up to 110 RBs are supported.
It is, however, not possible to address (in particular, in DCI Format 0, Format 1, or Format 3) another bandwidth than the one already used for the PDCCH control channel.
Furthermore, according to current specification (known as Release-8), only selected downlink (or uplink) system bandwidths are supported for being. For a frequency division duplex (FDD) scenario, these are for example 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. That is, only one of these six standardized bandwidths may be allocated both to any control channel and any data channel (in uplink or in downlink).
Therefore, standardized downlink (or uplink) system bandwidths may lead e.g. to violations of emission limits (if selected too wide) or do not fully exploit the available spectrum (if selected too narrow), which applies for example in typical coexistence situations. Consequently, deployment situations may arise, where at least the downlink (or uplink) system bandwidth cannot be matched efficiently by one of the standardized system bandwidths, e.g. by one of the six LTE Release-8 system bandwidths. Thus, arbitrary downlink (or uplink) system bandwidth scaling is not feasible according to current specification (e.g. LTE Release-8).
Namely, using a smaller (undersized) standardized downlink (or uplink) system bandwidth drastically reduces spectral efficiency, while using a larger (oversized) standardized bandwidth is simply not possible due to regulator's requirements and emission limits.
For example, if an LTE Release-8 radio access network is rolled out with 3 MHz downlink bandwidth in a spectrum block of 4.2 MHz, the downlink bandwidth to be allocated to control and data channels is at most 3 MHz (since the next higher standardized bandwidth of 5 MHz is already too large). Thus, as is evident from the above, the usage of a bandwidth (or a combination of bandwidths) being smaller than the available bandwidth reduces spectral efficiency both in uplink and in downlink.
Accordingly, there does not exist any feasible solution to the above drawbacks and requirements, which is mainly due to the (widespread) allocation positions of control channels and the binding to a limited set of standardized bandwidths.